1. Field of the Invention
This invention relates to an ink jet printer. More particularly, it is concerned with improvement in the construction of an ink tank for the ink jet printer.
2. Description of Prior Art
The construction of a conventional monochromatic ink jet printer is as shown in FIGS. 1 and 2 of the accompanying drawing, in which a reference numeral 1 designates an ink jet nozzle which is made of a glass tube, or the like. A piezoelectric element 2 in a hollow cylindrical form is fitted on and around the outer periphery of this ink jet nozzle 1. The forward distal end of the ink jet nozzle 1 is constricted to form an ejecting nozzle 1a, while the rear distal end part thereof is connected with one end of a tube 3. The other end of the tube 3 is immersed in ink 5 stored in a sub-tank 4 for the ink. A filter 6 is provided on this lower end part of the tube 3. A lid 7 is fitted on the top of this sub-tank 4 to render it air-tight in general. An air layer 4a with a predetermined volumetric space is formed in the top portion of the sub-tank 4.
Further, the sub-tank 4 is connected with one end of a flexible tube 8 through a connecting member (or portion) 8a, while the other end of the flexible tube 8 is connected with a main ink tank (not shown in the drawing). Furthermore, above the connecting member 8a, there is provided another connecting member 9a, to which one end of an ink suction tube 9 is connected. The other end of the ink suction tube 9 is connected to a negative pressure source (not shown in the drawing).
The ink jet nozzle 1 and the sub-tank 4 of the above-described construction are mounted on a carriage (not shown) in opposition to a platen 10. The printing ink is ejected from this ink jet nozzle 1 by contraction of the piezo element 2 upon electric conduction to the piezo element in accordance with a control signal, and the recording is effected on a recording sheet which is held on and led out by the platen 10.
In the ink jet printer of such construction, in order to prevent non-ejection of the ink from the ink jet nozzle 1 from taking place, a contrivance is made such that, when the non-ejecting condition occurs, or immediately before start of the printing operation, a cap (not shown in the drawing) is fitted at the distal end of the nozzle to suck out ink from it, thereby maintaining a regular ink feeding condition at the nozzle end so as to enable accurate printing operation to be carried out every time. Further, the ink 5 within the sub-tank 4 is drawn out by the ink suction tube 9 so as to constantly maintain the top surface of the ink at a level substantially flush with the connecting portion 9a. The suction of the ink is done, in most cases, in synchronism with the recovery operation to get rid of the above mentioned non-ejecting condition of the ink.
The ink jet printer shown in FIGS. 1 and 2 is an example of performing recording operation using a single color such as, for example, black. If, however, polychromatic printing is to be done by use of various colors such as, for example, yellow, cyan, magenta, etc., it becomes necessary, as a matter of course, to provide sub-tanks 4 and ink jet nozzles 1 for the number corresponding to the colors of the ink, each tank having the same structure.
However, when a plurality of sub-tanks are mounted on one and the same carriage, a large space becomes necessary to receive all these sub-tanks and the weight of the carriage as a whole increases with the consequent necessity for use of an electric motor, etc., having a large driving power for drive-control of the carriage. With increase in weight of the carriage as a whole, the inertia of the carriage becomes great accordingly. As the result, a complicated control is needed when the carriage is to be driven to an accurate position or to be caused to start, which disadvantageously results in slowing down the recording speed and in an increased manufacturing cost.